The present invention relates generally to semiconductor integrated circuit packaging and, more particularly to semiconductor device packages that incorporate an interposer.
Certain semiconductor packages, such as Ball Grid Array (BGA) packages, include one or more integrated circuit (IC or “chip”) dies or other active components electrically coupled to solder balls by way of a substrate. The substrate includes one or more interconnected, patterned metal layers sandwiched between insulating layers. The metal layers electrically connect contact pads on the die to respective solder balls on the exterior of the package. The die is encapsulated by a polymer molding compound to protect the die and one side of the substrate from environmental contaminants. The solder balls on the exterior of the encapsulated die/substrate serve as input and output (I/O) connections to the die and are typically arranged in rows and columns on the bottom of the BGA package for mounting the BGA package on a printed circuit board (PCB).
Compared to other types of semiconductor packages, BGA packages can advantageously provide a larger number of electrical connections than other types of packages, such as quad flat no lead (QFN) packages, and are therefore widely used for dies requiring many I/O connections, such as high-performance microprocessors, large field-programmable gate arrays, or the like.
Due to manufacturing limitations on the minimum size of features on a substrate, the contact pads on the die are usually much closer together (i.e., are more closely pitched) than corresponding conductors can be placed on a typical substrate. To address this issue, an interposer is placed between the die and the substrate to laterally route signals from the closely pitched die pads to the more widely pitched substrate contact pads.
The interposer, typically made of silicon or glass, has, on a first or obverse side, a set of contact pads that are aligned to respective die bond pads. On a second or reverse side of the interposer is a set of bond pads that are aligned with respective bond pads on the substrate. Conductive traces, usually on the first side of the interposer, and metal through-hole vias in the interposer provide signal paths from the first-side bond pads to the second-side bond pads. The conductive traces route signals between the vias and the respective bond pads on the die. Exposed ends of the vias are typically used as the bond pads on the second side of the interposer.
A first set of solder balls or the like connect the die bond pads to the bond pads on the first side of the interposer, and similarly a second set of solder balls or the like connect the bond pads on the second side of the interposer to the bond pads on the substrate. The interposer, along with the die and the above-mentioned bond pads on the substrate, is encapsulated by the mold compound.
The typical BGA package described above can be expensive to make. For example, the materials and processes used to make the silicon or glass interposer might make up a significant portion of the overall cost of the BGA package. More specifically, the interposer material itself is relatively expensive, and the process used to make the metal vias in the interposer, such as by plating, is expensive and time-consuming.
Further, because (i) silicon or glass has a substantially different coefficient of thermal expansion (CTE) than the substrate material (typically a multilayered dielectric formed from layers of woven glass embedded in an epoxy, e.g., FR-4) and (ii) the lateral dimensions of the interposer are approximately the same as that of the substrate, reliability of the BGA package might be degraded because the solder ball connections between the interposer and the substrate might crack as the temperature of the package cycles.
Accordingly, it would be advantageous to have a BGA package with improved reliability that can be less expensive to manufacture than conventional BGA packages.